In recent years, with rapid spread of information-related equipment or communication equipment such as PCs, video cameras, mobile phones, etc., development of batteries used as the power source thereof is considered to be important. Among these batteries, a lithium ion battery has attracted attention due to its high energy density.
In a lithium ion battery that is currently commercially available, since an electrolyte containing a flammable organic solvent is used, attachment of a safety device that suppresses an increase in temperature at the time of short circuit, and improvement in structure and material in order to avoid occurrence of short circuit is required. On the other hand, it is thought that, since a lithium ion battery obtained by allowing a battery to be totally solid by using a solid electrolyte instead of liquid electrolyte does not use a flammable organic solvent in a battery, simplification of a safety device can be attained, and a production cost can be saved or productivity can be improved.
As the solid electrolyte used in a lithium ion battery, a sulfide solid electrolyte is known. As the crystal structure of a sulfide solid electrolyte, various structures are known. As one of such crystal structures, an argyrodite type crystal structure can be given. Patent Documents 1 to 5 or Non-Patent Documents 1 to 3, etc. disclose an argyrodite type crystal structure comprising one type of a halogen. Further, Non-Patent Documents 4 and 5 report a solid electrolyte having a composition of Li6PS5Cl1-xBrx, and disclose an argyrodite type crystal structure comprising two types of halogen. Some of the argyrodite type crystal structures have high lithium ion conductivity. However, further improvement in ionic conductivity is required. In addition, in general, a sulfide solid electrolyte has a problem that there is a possibility that it generates hydrogen sulfide when reacted with moisture contents in air.